RadRichTextBox uses format providers in order to open and save documents in different formats. There are also data providers built on top of some of the format providers in order to provide the means for data-binding.
There are examples showing how the providers can be used with documents stored on the server in this forum post. Both examples use RIA services; the difference is that the RiaPersistingInOpenXML demo uses DocxFormatProvider in order to save the documents in docx format and the other sample uses a data provider.
All the best,
the Telerik team
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